Oxazolines are five-membered cyclic compounds having an endo-imino ether (AN¼¼CAOA) group. They belong to one of the classes of cyclic imino ethers, which contain cyclic endo- and exo-imino ethers of 5-, 6-, and 7-membered rings. An early stage of chemistry of oxazolines including their preparation, reactions, and applications was extensively reviewed previously. Historically, oxazolines have been known since the end of 19th century. The first attempt of the preparation was made in 1884 via dehydrohalogenation of allyl urea, resulting in detection of a new cyclic compound but failing to deduce its correct chemical structure. Five years later, the first successful synthesis of oxazolines was reported and then the chemistry of oxazolines started to be increasingly investigated.
Oxazolines have three structural isomers; 2-oxazoline, 3-oxazoline, and 4-oxazolines. Among them, 2-oxazolines are by far the most well-known and extensively studied. The formation of an oxazoline ring was postulated in the cyclodehydration at peptide linkages constituted from the a-amino-b-hydroxy acids, serine, or threonine. 2-Substituted-2-oxazolines were formed via the cyclization of an acyl derivative of a-amino acid with dehydration, the reaction of an amino alcohol with a carboxylic acid, the cyclization of a b-haloalkylamide via dehydrohalogenation, and so forth. Chemistry of these hetero-cyclic compounds was widely studied by reactions with a variety of compounds. Oxazoline is used in polymer chemistry, to make amino alcohols, is stable, starting compound for making ionic liquids, pharma-compound that reduces appetite and facilitates weight loss.
U.S. Pat. No. 4,105,669 discloses manufacture of 2-amino-1-alcohols carried out by reacting the hydroxyketone with ammonia at from about 0° to 120° C., preferably at from room temperature 20° C. to 80° C., at a pressure of from atmospheric pressure to about 300 bars, preferably up to about 100 bars. The reaction may be carried out without using extraneous solvents. But reaction takes place in two steps with less conversion and selectivity about less than 85 percent and also reaction took place in harsh conditions.
U.S. Pat. No. 7,619,119 discloses two steps process for converting glycerol to an amino alcohol product involving reacting glycerol with a metal catalyst to obtain hydroxyacetone and reacting the hydroxyacetone with an amine compound to obtain an adduct that is then reduced using a reducing agent to obtain an amino alcohol product. The metal catalyst is a catalyst selected from the group consisting of copper, chromium, nickel, zinc, cobalt, manganese, silicon, aluminum, copper chromite, copper zinc, oxides thereof, and combinations of any thereof.
U.S. patent application no. 20080045749 discloses two steps industrial process for the alternating production of propylene glycol or an amino alcohol product from glycerol comprising: 1) reacting glycerol with a metal catalyst to obtain hydroxyacetone; 2) optionally reacting the hydroxyacetone with an amine compound to obtain an adduct; and 3) reducing the hydroxyacetone or the adduct using a reducing agent to obtain a product, wherein the product is propylene glycol when the hydroxyacetone is reduced with the reducing agent and the product is an amino alcohol product when the adduct is reduced with the reducing agent. The metal catalyst is a catalyst selected from the group consisting of copper, chromium, nickel, zinc, cobalt, manganese, silicon, aluminum, copper chromite, copper zinc, oxides thereof, and combinations of any thereof.
U.S. Pat. No. 8,809,593 discloses a process for the preparation of the hydroxyacetone or 1,2 propylene glycol. This process is catalyzed by metal catalysts that results in 80 to 100% selectivity towards conversion of glycerol to hydroxyacetone (acetol) or 1,2 propylene glycol. The metal catalysts are selected from the group Cu, Cr, Al, Ba, Zn, Si, Zr, Mg or in combinations thereof.
Article titled “Study on the reactions of ammonia precursors and alpha-hydroxy carbonyl compounds (iii), identification of novel 3-oxazolines” by Ken Shu et al. product formulation. PD93 188, 7 Jul. 1993. The major compounds formed from the reactions between alpha-hydroxy carbonyls and ammonium hydroxide has been identified by MS, IR, NMR and synthesis as 3-oxazolines.
Article titled “Simultaneous glycerol dehydration and in situ hydrogenolysis over Cu—Al oxide under an inert atmosphere” by Rasika Mane et al. published in Green Chemistry, 2012,14, 2780-2789 reports dehydration of glycerol and in situ hydrogenolysis in presence of Cu—Al oxide catalyst. Substantial enhancement in 1,2-Propane diol selectivity (75%) was achieved for an aqueous bio-glycerol feed over the same catalyst for 50 h of testing.
Article titled “Continuous dehydration and hydrogenolysis of glycerol over non-chromium copper catalyst: laboratory-scale process studies” by Rasika Mane et al. published in Organic Process Research & Development, 2012, 16(5):1043-1052 reports a non-chromium Cu:Al catalyst was developed for glycerol dehydration under N2 atmosphere to acetol and hydrogenolysis to 1,2-propanediol (1,2-PDO). Among the various copper-based catalysts screened in this work, Cu:Al-1 catalyst showed the highest activity and acetol selectivity in water medium.
Article titled “Dehydration of glycerol to acetol via catalytic reactive distillation” by Chuang-Wei Chiu et al. published in AIChE Journal, 2006, 52 (10), 3543-3548 reports dehydration of glycerol in the presence of various metallic catalysts including alumina, magnesium, ruthenium, nickel, platinum, palladium, copper, raney nickel, and copper-chromite catalysts to obtain acetol in a single-stage reactive distillation unit under mild conditions. High-acetol selectivity levels (>90%) were achieved using copper-chromite catalyst, and operating in semi-batch reactive distillation mode.
Article titled “Thermal conversion of glycerol to value-added chemicals: pyridine derivatives by one-pot microwave-assisted synthesis” by DuyguBayramoglu et al. published in Turkish Journal of Chemistry, 2014, 38: 661-670 reports one-pot syntheses of the value-added heterocyclic compounds 3-methylpyridine and pyridine using a renewable chemical, glycerol, were achieved in acidic medium by thermal conversion reactions. Condensation/cyclization reactions of the thermal degradation products of glycerol were investigated in situ using different ammonia and acidic moiety producing inorganic ammonium salts under pyrolysis or microwave heating conditions. But reaction takes place in harsh conditions.
Article titled “A review of acetol: application and production” by MohdHanif Mohamad et al. published in American Journal of Applied Sciences, 2011, 8 (11), pp 1135-1139 reports the production of acetol from glycerol is greatly influenced by the presence of catalyst. The most famous catalyst used in the production of acetol from glycerol is the metal supported acidic catalyst. In nitrogen flow, unreduced Cu—Al2O3 decreases the conversion and increases acetol selectivity with time on stream. Meanwhile, when CuAl2O3 was subjected to hydrogen reduction, it is fully converted to glycerol and acetol selectivity increases with time on stream for the first 5 hours.
The above reported processes in prior arts involve multi steps with low yields. Therefore there is a need to develop a single step one pot process with high yields.